The present invention relates to a roll stand for a planetary rolling mill of the type having stands, stationary support bodies with rolling segments mounted in chocks, and intermediate and work rolls mounted in cages and rotating around the support bodies.
In a planetary rolling mill of the foregoing type, known as a Platzer planetary rolling mill after its inventor, the working rolls are brought to rest, upon rotation around the stationary support members in opposition to a centrifugal force, against the intermediate rolls and the latter are brought to rest against the support bodies. The surface of the support bodies represents, except for a small region of the shaping zone, a precise cylindrical surface. Within this region of the shaping zone, the rolling surface differs from an exact circular shape in order to assure a dependable, i.e. groove-free, surface of the stock rolled. This roll geometry differs from a precise cylinder surface, produced, for reasons of wear, by means of rolling segments inserted in the support bodies. These rolling segments, which form the rolling path for the intermediate rolls, are made of hardened steel and are fastened replaceably in recesses in the support body.
The rolling segments are subjected to very high mechanical loads since in the shaping zone the radial rolling forces in the stationary support bodies are conducted over them. During the shaping, upon the rolling of the supporting rolls on the rolling segment, high hertzian pressures are produced. With 24 support rolls per cage, each rolling segment is rolled over 24 times upon each rotation of the cage.
With a customary cage speed of rotation of 120 rpm and a load of about 85 t there results a life of a segment of about 25 hours. An incipient formation of grooves indicates that regrinding of the segment is necessary. For the regrinding, the set of rolls must be removed from the stand so that the rolling segment can be dismounted. Five working rolls and five backup rolls from each set must be removed before the rolling segments can be dismounted. They are fastened, for instance, by screws in the support body. The old rolling segment is removed and reworked on a surface grinding machine. Another completely reground rolling segment is installed into the set of rolls and the latter is supplemented again with the five backup and working rolls. This requires a large amount of labor and time, extensively limiting the availability of the planetary rolling mill if the rolling segments must be removed and reground after every 25 hours.
In addition to this, while it is true that in the case of smaller roll stands it is still possible to remove and install the working rolls by hand, for the handling of the rolling segments, however, a light crane is required. In the case of medium size and larger roll stands, however, in which the working rolls weigh up to 600 kg, suitable hoists are required, which leads to increased investment costs and to a lengthening of the removal and installation times.
With a production machine or installation, long standstill times are not acceptable. This applies, in particular, to systems with high investment costs. The purpose of a roll stand must therefore be to lengthen both the times between the required replacement of the work rolls and the rolling segments and to reduce the time for replacement or reinstallation.
Since, by the grinding of working rolls in an installed condition, it has been possible to substantially reduce the corresponding amount of work and increase the time between the changing of the working rolls to about 100 hours, the rolling segments with a life of about 25 hours are a determining time and cost factor.
An object of the invention is to substantially increase the times between the changing of the rolling segments and to reduce the work connected therewith.
The foregoing object is achieved in a roll stand of the aforementioned type in the manner that the chocks have a square basic shape and each support body, instead of being equipped as previously with one, is provided with four rolling segments distributed uniformly over the circumference, and is furthermore provided at each end with a rolling ring. By a roll stand developed in this manner the steps for the removal of the worn rolling segments and installation of the reground rolling segments, which are customarily necessary about every 25 hours and are very time-consuming, become superfluous.
These steps are: (i) removal of the two support bodies from the roll stand; (ii) removal of in each case five working rolls and five intermediate rolls; and (iii) replacement of the rolling segments and reinstallation in reverse sequence.
In a roll stand in accordance with the invention, those rolling segments which are in use become so worn after about 25 hours of operation that they must be replaced, even in the case of optimal heat treatment. Since the support body however is equipped with 4 rolling segments distributed uniformly on the periphery, the support bodies are merely moved out of the roll stand, turned 90.degree., and reinstalled upon every fourth regrinding of the work rolls, when they, in any event, must be removed.
By the provision of four rolling segments per support body which are brought into use one after the other, a further advantage is obtained. The removal and installation of in each case 5 work rolls and 5 intermediate rolls, as is otherwise necessary for the changing of the rolling segments, is dispensed with since this operation can be carried out precisely when the work rolls are finally worn out completely after 16 regrindings, i.e. such rolls have reached the smallest permissible diameter and must be replaced by new ones.
In the Platzer roll stands constructed up to the present time the working rolls are pressed against the intermediate rolls by means of packs of disk springs upon rotation around the support bodies in a direction opposite the centrifugal force, and these intermediate rolls are held in continuous contact with the cylindrical surface of the support bodies. In the region of the rolling segment with its geometry that differs from a precise cylindrical surface, the rolls are pressed by the rolling force. In the case of the roll stand of the invention, upon the customary speeds of rotation there would be, as a result of the geometry, a brief lifting followed by impact-like replacing of the intermediate rolls on the surface of the support body in the region of the three additional roll segments, and therefore wear. In the case of the invention, therefore, it is assured by a design measure that the lifting of the rolls is definitely avoided upon the rolling over of the three rolling segments which are not in engagement. For this there are suitably two rolling rings, namely one on each side of the support body. By means of these rolling rings the intermediate rolls are guided over a dependable circular path also in the region of the three rolling segments which are not in engagement, so that impact-like application of the intermediate rolls is avoided. In the working region the rolling rings have recesses so that the rolls can rest here against the flats of the rolling segments.
The chocks are of a square basic shape, as a result of which exact positioning of the rolling segments which are arranged 90.degree.. Removal and installation of the rolling segments is unnecessary at this time as is the removal and reinstallation necessary for the purpose of, in each case, 5 working rolls and 5 intermediate rolls. The result is furthermore obtained that the replacement of the 4 pairs of worn rolling segments is effected when the working rolls must be replaced so that no additional work and installation for this expense results.
An alternative embodiment of the invention resides in the fact that the chocks are developed in an octagonal shape and each support body has eight rolling segments. This has the advantage that the time between the necessary replacement of the rolling segments can be doubled.
An advantageous further development of the invention resides in the fact that the two rolling rings of a support body can be turned by a turning device with respect to the support body and clamped against the support body by clamping means. In this way it is possible to effect, in a simple and rapid manner, the rotation of the rolling rings with respect to the support body by 90.degree.. This rotation is necessary in order that the recesses of the rolling rings again agree with the working zone. By these means, the rolling rings are turned without removal or mounting work, under the application pressure exerted by the packs of spring disks. For turning the rolling rings, clamping devices (preferably four in number) that are arranged between the rolling segments, are loosened, by means of which the rings are clamped fast against the support bodies during operation.
The two rolling rings of each support body are advisedly turned synchronously by the required 90.degree.. For this purpose, the rolling rings are provided with an inner toothing on the side facing the support body. Into this inner toothing there engage drive pinions that are fastened on a common shaft extending within a hole in the support body and mounted for rotation therein. The drive is effected by a drive unit with a stepping motor arranged in one of the chocks, so that precise positioning in the installed condition can be effected without measuring or a control device and without visible verification. In order to be able to keep the size of the stepping motor small, a hydraulic booster as well as a self-locking gearing is arranged between it and the pinion. This self-locking gearing (for instance, a worm gearing) has the advantage that in this way shaking loose in operating condition, i.e. a gradual overcoming of the clamping force of the clamping device, is definitely avoided.
The clamping devices are advantageously developed as clamping cylinders which are arranged in holes in the support body. The clamping force is produced by disk springs, and loosening for the turning of the rolling rings is effected by the action of pressure on the cylinder chamber. The piston rod is provided on its free end with a head or block which engages in an annular groove in the rolling segment, which groove is worked into the surface facing the support body. Upon the release of the cylinder from the load, the spring force of the disk springs holds the rolling ring firmly against the support body.
In order to make the installation and removal of the support bodies together with their chocks as simple as possible, the edge lengths or the distance apart of the side surfaces of the latter are smaller than the outside diameter of the planet set. For each chock, two ledges are provided which are screwed, corresponding to the position of installation, to the vertical side surfaces of the chocks and are correspondingly mounted upon the turning of the support body by 90.degree.. This is the only manual action upon the turning of the support bodies.
In order to facilitate the turning in each case of the support bodies, they can be provided on each end with pivot pins which extend outward beyond the chocks. In this way, turning of the support bodies after the removal of the planet rolls from the stand by 90.degree. is possible in a simple manner in a turning device which is located alongside the roll stand.
In a further embodiment, the chocks are provided with an octagonal basic shape, rather than a square shape, and each support body is provided with eight rolling segments distributed uniformly on its periphery, rather than four.